I think there's a misunderstanding. They aren't removing themselves from Bitcoin, they are just not offering exchange uses anymore. They are going to run a sidechain for settling payments. So it's not about being against BTC, they just won't be taking part in the actual exchange.
This.
Here's the related CD article that sheds some light on the matter:
http://www.coindesk.com/circle-bitcoin-shift-isnt-what-it-seems/...
Circle has not "pulled the plug" on bitcoin, as many have reported.
Users can still store it in their Circle account and send it to others. Bitcoin will continue to be a settlement token and Spark, the new protocol unveiled this week, is partly based on the bitcoin system.
...
Anyone knows what will happen if I send btc to an old circle btc address after having converted to local currency (and can't convert back to Bitcoin)? If such deposits go through and get auto-translated to fiat, then you could still use circle to sell btc.